In order to provide safety to drivers and passengers in automobiles, an important consideration is resistance to side impacts, especially at the door areas. In order to provide intrusion resistance in the past, steel beams or other metal framing were connected to doors to provide the necessary impact resistance.
With the emphasis on gasoline savings, automobiles have been made lighter by the replacement of plastic parts for many of the metal parts. Plastic parts, per se, are generally weaker than their corresponding metal parts. Despite the use of plastic parts, the safety standards especially those relating to doors and their resistance to intrusion upon impact, have not been relaxed.
To establish standards, it is generally necessary to measure the distances of intrusions or penetration of a door for certain levels of force. For example, the standard may limit the degree of penetration or intrusion of an automobile door to six inches when an average load of 2250 pounds is applied. Likewise, the intrusion distance may be limited to twelve inches when an average force of 3500 is applied. A maximum force of 7000 pounds or two times the automobile weight, must be reached within the first eighteen inches of penetration. Of course these standards are variable. The desired result is to achieve the maximum practical safety against intrusion while at the same time, making the doors relatively light in weight.
Molded plastic doors used heretofore have included chopped glass fibers approximately one inch long. Such materials used heretofore have little elongation or toughness and have low strength.